I asked permission from the Prophet ﷺ and entered, slipping between him and his shirt.I said, "Messenger of Allah, what is the thing that may not lawfully be withheld?"He replied, "Water."I said, "Messenger of Allah, what is the thing that may not lawfully be withheld?"He replied, "Water."I said, "Messenger of Allah, what is the thing that may not lawfully be withheld?"He replied, "That you do good is better for you."
حدثنا وكيع قال حدثنا كهمس بن الحسن عن سيار بن منظور الفزاري عن أبيه
استأذنت النبي ﷺ فدخلت بينه وبين قميصه قال فقلت يا رسول الله ما الشيء الذي لا يحل منعه قال الماء قلت يا رسول الله ما الشيء الذي لا يحل منعه قال الماء قال قلت يا رسول الله ما الشيء الذي لا يحل منعه قال أن تفعل الخير خير لك
Its chain of transmission is daif, due to the unknown status of Buhaysah, though it has been said that she was a companion, and according to this view the hadith is sahih. It is found in Abu Dawud with his chain and wording, 2/127, number 1669, in the chapter on zakat, on what may not be withheld, and similarly in Darimi, 2/349, number 2613.